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[PATCH] ARM: 2664/2: add support for atomic ops on pre-ARMv6 SMP systems 

Patch from Nicolas Pitre

Not that there might be many of them on the planet, but at least RMK
apparently has one.

Signed-off-by: Nicolas Pitre
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
hifive-unleashed-5.1
Nicolas Pitre 2005-06-08 19:00:47 +01:00 committed by Russell King
parent aeabbbbe12
commit dcef1f6346
3 changed files with 68 additions and 5 deletions
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16
arch/arm/kernel/entry-armv.S
View File

@ -269,7 +269,7 @@ __pabt_svc:
add r5, sp, #S_PC
ldmia r7, {r2 - r4} @ Get USR pc, cpsr
#if __LINUX_ARM_ARCH__ < 6
#if __LINUX_ARM_ARCH__ < 6 && !defined(CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG)
@ make sure our user space atomic helper is aborted
cmp r2, #VIRT_OFFSET
bichs r3, r3, #PSR_Z_BIT
@ -616,11 +616,17 @@ __kuser_helper_start:
__kuser_cmpxchg: @ 0xffff0fc0
#if __LINUX_ARM_ARCH__ < 6
#if defined(CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG)
#ifdef CONFIG_SMP /* sanity check */
#error "CONFIG_SMP on a machine supporting pre-ARMv6 processors?"
#endif
/*
* Poor you. No fast solution possible...
* The kernel itself must perform the operation.
* A special ghost syscall is used for that (see traps.c).
*/
swi #0x9ffff0
mov pc, lr
#elif __LINUX_ARM_ARCH__ < 6
/*
* Theory of operation:

49
arch/arm/kernel/traps.c
View File

@ -464,6 +464,55 @@ asmlinkage int arm_syscall(int no, struct pt_regs *regs)
#endif
return 0;
#ifdef CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG
/*
* Atomically store r1 in *r2 if *r2 is equal to r0 for user space.
* Return zero in r0 if *MEM was changed or non-zero if no exchange
* happened. Also set the user C flag accordingly.
* If access permissions have to be fixed up then non-zero is
* returned and the operation has to be re-attempted.
*
* *NOTE*: This is a ghost syscall private to the kernel. Only the
* __kuser_cmpxchg code in entry-armv.S should be aware of its
* existence. Don't ever use this from user code.
*/
case 0xfff0:
{
extern void do_DataAbort(unsigned long addr, unsigned int fsr,
struct pt_regs *regs);
unsigned long val;
unsigned long addr = regs->ARM_r2;
struct mm_struct *mm = current->mm;
pgd_t *pgd; pmd_t *pmd; pte_t *pte;
regs->ARM_cpsr &= ~PSR_C_BIT;
spin_lock(&mm->page_table_lock);
pgd = pgd_offset(mm, addr);
if (!pgd_present(*pgd))
goto bad_access;
pmd = pmd_offset(pgd, addr);
if (!pmd_present(*pmd))
goto bad_access;
pte = pte_offset_map(pmd, addr);
if (!pte_present(*pte) || !pte_write(*pte))
goto bad_access;
val = *(unsigned long *)addr;
val -= regs->ARM_r0;
if (val == 0) {
*(unsigned long *)addr = regs->ARM_r1;
regs->ARM_cpsr |= PSR_C_BIT;
}
spin_unlock(&mm->page_table_lock);
return val;
bad_access:
spin_unlock(&mm->page_table_lock);
/* simulate a read access fault */
do_DataAbort(addr, 15 + (1 << 11), regs);
return -1;
}
#endif
default:
/* Calls 9f00xx..9f07ff are defined to return -ENOSYS
if not implemented, rather than raising SIGILL. This

8
arch/arm/mm/Kconfig
View File

@ -422,3 +422,11 @@ config HAS_TLS_REG
assume directly accessing that register and always obtain the
expected value only on ARMv7 and above.
config NEEDS_SYSCALL_FOR_CMPXCHG
bool
default y if SMP && (CPU_32v5 || CPU_32v4 || CPU_32v3)
help
SMP on a pre-ARMv6 processor? Well OK then.
Forget about fast user space cmpxchg support.
It is just not possible.